From Saint-Nom to Poissy through the forests of Marly and Tailles d'Herbelay

Starting point and access: Saint-Nom-la-Bretèche station – Marly Forest.
- Transilien - Line L, terminus of the section between Paris Saint-Lazare and Saint-Nom-la-Bretèche.
Take the only exit, at the front of the train.

Red and white markings

(S) At the end of the platform, turn left to cross the level crossing. Follow the road uphill, passing a small car park on the left. Take the bridge over the railway line. Turn immediately right and follow a path that leads into the woodland. Stay on the main path and ignore any vague side paths. You’ll come to a junction, beyond which, a few dozen metres away, you can make out a large crossroads.

(1) Turn left here and you will soon reach another junction (signposted “Étoile de la Maison Rouge”): go straight on. Heading west or west-south-west, climb steadily up the path, which gradually widens. At each junction, go straight on.

(2) At the top, at a junction (Étoile de Dryade), take the first path on the right. At the next junction, near a road (plot no. 106), turn right. Stay on the main path, which curves to the right. Reach the Croix Saint-Michel.

(3) Then head down to the left onto a narrow path that starts at the foot of the cross and two small wooden posts (one of which was on the ground in June 2020). At the junction that appears immediately, take the middle path (signposted). Head straight on northwards, going downhill and then uphill. Cross a cycle path and then the D98 ( a very busy road) and continue along the path opposite.

No signposting

At the first junction, turn left (let the^GR®®1continue straight ahead). At the next junction, go straight on. You’ll come out onto a path; follow it to the left for a few metres until you reach a junction at the boundaries of plots nos. 10A, 10B and 13 (at this junction, some of the paths shown on the map do not exist… or no longer do).

(4) Then take a path heading north-west, which starts just to the right of the tree marked No. 10A. Further on, you will find the ‘horseshoe’ symbol for a bridle path on the right-hand side. At the next junction (elevation 181, signpost), continue straight on along Route Hardouin. At the junction in a sort of small clearing, continue straight on along a wide path. Walk past a pond on your right.

At the next junction (Étoile du Gros Érable; plot no. 23, blue double-sided signs), take the path opposite. Immediately cross a wide grassy track and continue along the path, which appears to be poorly maintained but is well marked. Walk alongside a beautiful, open-plan forest on your left, then continue through denser undergrowth.

(5) You’ll come out onto a small road (with no traffic) and follow it to the right. At the next junction (elevation 173), leave the tarmac, go down the path opposite and you’ll soon reach a junction at the boundaries of plots nos. 23, 35 and 51. Then turn left and walk along a fenced plot on your left.

Red and white markings

At the crossroads (Étoile du Chêne de Retz; bench), veer right, immediately ignore a path branching off to the right and follow a track, leaving a tree marked no. 36 on your right. Winding your way along, you’ll reach a junction with large beech trees.

Yellow markings

(6) Then turn right (let the^GR®®1continue straight on). Ignore a vague path on the right and head downhill. At the crossroads (walls, boundary stone), go straight on between two fences and walk alongside a golf course on your right. Pass the entrance gate to the Désert de Retz and walk alongside a wall on your right. Return to the tarmac, turn right at the roundabout and walk alongside the long building of the Ferme de Retz on your right.

No signposting

(7) At Chemin des Jongleurs, leave the tarmac and take a sharp left (chain) onto a path that enters the Tailles d’Herbelay Departmental Forest. Climb steadily along a fence on the left and ignore all tracks on the right. At a Fork in the road, follow the path to the right, which continues on roughly level ground. Pass a boundary stone on the right-hand side and arrive at a crossroads.

(8) Then take the^second path on the right (north-west; pass a picnic table on your right). At the next junction, go straight on. Pass through a forest gate and head downhill. At the junction (marker), turn right. On your left, walk along garden fences or a hedge in turn. Keep heading north-east and ignore all turn-offs to the right.

You will come out onto a road; cross it at the pedestrian crossing and follow it to the right along a path protected by a railing and reserved for pedestrians and cyclists. Enter Chambourcy. Go round the roundabout on the left, cross Chemin de Saint-Barthélémy, take the next street (not signposted here) and walk alongside a fenced-off reservoir on your left.

Yellow markings

(9) At the corner by the fence (EDF substation), turn left onto a path, which is wide and grassy at first, then narrows. Pass through a metal gate, continue downhill on the tarmac and ignore all the turnings on the left. At the bottom, turn right. Pass a dead-end on the left and continue for about fifty metres. When the street turns left, continue straight ahead onto a cobbled street, the Grande Rue. Go straight on until you reach the church.

Red and yellow markings

(10) Then go down a flight of steps on the left. Cross an esplanade, leaving the town hall on your right, and go down another flight of steps. At the bottom, turn right and go down a tarmac lane. At the Stop sign, turn left. At the roundabout, continue straight ahead. At the end of the street, turn right towards Poissy and go straight on until you reach the traffic lights.

Cross the D113 at two successive sets of traffic lights and continue straight ahead, on the right-hand pavement. At the stop sign, go straight on. Pass beneath the Croix de la Laye and take the bridge over the A14. At the sign marking the entrance to Poissy, turn right and enter the Saint-Germain-en-Laye State Forest.

No signposting

(11) After about 50 metres, at a three-way junction, take the left-hand path (leaving the^GRP®®). Immediately turn right onto this path and ignore a left-hand turn towards a wall. At the junction (plot no. 231), turn left. At the next junction, take a path on the right.

Red and yellow markings

At the end, rejoin the^GRP®® and follow it to the left. Leave the forest (sign with map), go down a flight of steps, cross Rue Beauregard and first turn left then right to follow Rue du Docteur Labarrière. Cross Rue des Grands Champs and go straight on.

No markings

(12) At the corner of No. 16, turn left onto the Petite Sente des Culezets (take care to spot this start). The path, which is very narrow, first turns right then left before opening out onto a street: follow this street to the right and downhill. At the end, first turn left then right to follow the Petite Sente des Culezets again, which is much wider here. At the end, turn left and walk along the cemetery wall. You’ll reach a crossroads at the corner of the cemetery (Poissy prison opposite on the right).

Red and yellow + red markings (very rare)

(13) Cross the junction, turning left then right, and head up Avenue Blanche de Castille on the left. Take the^first right, Avenue Christine de Pisan. At the end, turn right and follow the Enclos de l’Abbaye. After a right-hand bend followed by a left-hand bend, pass under a gateway. Further on, at the Toy Museum, pass under another gateway.

You will come out onto an avenue; follow it to the left. Cross at the first pedestrian crossing, at Rue de la Caserne, and turn left again. Take the^first right, Rue de l’Église, to reach the south entrance of the Collégiale Notre-Dame.

(14) Retrace your steps and, at the corner of the bell tower porch, turn right and cross a tree-lined square. At the end, first turn left then right to cross Rue Saint-Louis at the pedestrian crossing. Continue straight ahead onto Avenue Meissonier. Pass under the railway bridge, then turn right onto Cours du 14 Juillet. Follow the Seine to the Vieux Pont de Poissy (ruins on the left).

Ignore Rue de la Gare on the right and continue for a few dozen metres along the tree-lined riverbank. Then take the pedestrian crossing on the right, which allows you to cross a wide avenue in two stages. Pass the coach station on your left, turn right and head towards Poissy station (E).

To get back home:
- RER - Line A, towards La Défense and Paris.
- Transilien - Line J, towards Mantes-la-Jolie or Paris-Saint-Lazare.

Train timetables: see the Transilien website.

For motorists:
Park at least one vehicle in the car park at each of the two stations that are not on the same line. If using a single vehicle, you would need to change at La Défense Grande Arche or Paris Saint-Lazare.

Hiking boots recommended.

No water points identified along the route. Bars, restaurants and shops in the town centres of Chambourcy, before (10), and Poissy, between (14) and (E).

A detailed map is required (at the very least the one accompanying this description).

Warning:
Hikers are advised that the route runs close to the A13 motorway and that the heavy traffic there is certainly audible.

Walk completed by the author on 21 September 2019.

From (S) to (9), in the forest:
- Pleasant paths.
- A few remarkable trees.
- Saint-Michel Cross (18th century).

(10) In Chambourcy:
- Sainte-Clotile Church (17th–19th centuries).

From (14) to (E), in Poissy:
- Notre-Dame Collegiate Church (11th–16th centuries).
- Remains of the Old Bridge of Poissy (12th century).